Abstract: ¹¹C-methionine (MET), an amino acid, is the most widely used radiopharmaceutics which can reflect transport metabolism of amino acid in vivo, and synthesis of protein in tumor.¹¹C-METPET can be used for evaluation of brain tumor:detection of tumor, differential diagnosis between recurrence and radiation necrosis and early evaluation of response to treatment.Especially, for the definition of tumor margin and detection of low-grade tumors, PET with ¹¹C-MET is better than PET with ¹⁸F-FDG or other modalities such as CT and MRI.